Double-wall vessels are employed widely in low-temperature or cryogenic fields as containers for low-temperature fluids and generally comprise an inner vessel or wall and an outer vessel spaced from the inner vessel and surrounding same so that incursion of heat to the inner vessel is minimum. Such structures, therefore, have an inner wall member and an outer wall member which must be maintained in a spaced relationship to one another to prevent direct or conducted heat transferbetween.
In the case of Dewar flasks, for example, the inner vessels or wall and the other wall may be silvered to minimize radiation transfer heat therebetween while the space between the wall members is constructed so as to minimize convective heat transfer.
In general, the walls are relatively thin and hence support must be provided for the inner wall member upon the outer wall member.
Dewar flasks of the aforedescribed type are used generally for the storage or production of low boiling liquids, especially so-called liquefied gases, including liquid nitrogen or liquid helium.
In practice it has been found to be difficult to assemble such double-wall vessels because the setting of the space between the walls is ticklish and failure to provide effective spacing or proper support may result in tearing of one of the wall members at the mouth or neck of the flask. Furthermore, the problem is complicated by the fact that most effective thermal isolation is obtained with very thin walls and by the fact that the means spacing the walls from one another should not be thermally conductive.
In German patent document (Printed application - Auslegeschrift) DE-AS No. 1,186,088 the spacing is achieved with thin spacer bars of high strength material received in sleeves. Adjustment with these spacers is not simple and, since the bars are usually composed of metal, the thermal transport through the spacers is considerable.